Fixed retention of concrete objects against a suitable substrate occurs in many different situations. One example of such a situation is the fixed retention of concrete curbstones which rest on, for example, a road surface of asphalt and are fixedly retained therein.
Curbstones which are designed for such use are known in many different variations, in one such variation the curbstone having incast iron strips in whose free ends holes are provided which serve to accommodate the spikes fixedly retaining the curbstones. A further embodiment is provided with an elongated projection on the rear face of the curbstone in which there are cast plastic sleeves which in their turn serve to accommodate and guide those spikes which fixedly retain the curbstone to the substrate.
For reasons of strength, the above-mentioned types of curbstones are made of a relatively wet concrete mixture which contains amounts of large aggregates, often having a size up to 15-18 mm. The concrete mixture is cast in molds of steel, the concrete mixture being brought to such a compact and blister-free state as possible by means if vibration. Considerable problems are involved, in such a manner of manufacture, in casting various objects into the curbstone which objects may need extremely accurate alignment in relation to the rest of the curbstone, because of the necessary vibration. On the one hand, such an object must naturally, be fixedly retained at a sufficiently efficient level in the molding tool so as not to be deranged from its position during the vibration, and, on the other hand, a very liquid concrete slurry will be separated during the vibration operation and has an extremely troublesome tendency to penetrate into all nooks and crannies, for which reason, for example, a plastic sleeve cast into the concrete runs the risk of being filled with this concrete slurry.
The inventive concrete objects are manufactured in great quantities using automatic machinery. To allow that also the spikes be mounted automatically into the plastic sleeves it is necessary both that the concrete object itself has close tolerances and that the concrete object can be carefully positioned in relation to the mounting mechanisms for the spikes. Further, it is necessary that the plastic sleeves be positioned with close tolerances in the concrete object.